Gary, Skipp and/or anyone else, I'm just curious - where is the failure occurring in your PA? I was also running an MSR2000 (albeit on UHF) and I keep getting a failure at the harmonic filter on the antenna output side. (Kept melting the connection.) I've since taken the machine off the air and replaced it with a back-up. The backup has been happy as a clam for about 5 months, whereas the MSR would fail in about 4 - 6 weeks time.
If replacing parts in the PA will alleviate my troubles, can someone point me in the right direction? I'd be willing to scrounge up an old UHF Motorola Mitrek and cannibalize it to get rid of the headaches I'm suffering now. -----Original Message----- From: Gary [mailto:[EMAIL PROTECTED] Sent: Monday, January 03, 2005 7:55 PM To: [email protected] Subject: [Repeater-Builder] Re: MSR2000 PA Problems --- In [email protected], "skipp025" <[EMAIL PROTECTED]> wrote: > > > "Gary" <[EMAIL PROTECTED]> wrote: > > About a year and a half ago I replaced the whole board > > on my VHF MSR2000 110 watt NCD PA. (My PA had more > > problems than just the transistors) I used the PA board > > out of a 110 watt mitrek mobile. > > Tis' the cost effective way if you have the skills, > proper tools, bright lights, decafe coffee and knowledge.. > > > It took me an afternoon to do it as I recall. I had to > > remove the power control circuitry and change some > > values of some resistors on the input side of the mobile > > PA, but it still works great today with a nice clean output. > > The time required seriously depends on the model and > band of operation. Double the time when dealing with the > UHF ceramic substrates. > > > MSR2000 PA's are notorius for failing, especially the > > NCD units. > > What is an "NCD unit"? > > > You could not back the power down enough and still > > maintain a clean output, no matter how much air you > > blew on and out of the PA. > > ..? > > Power reduction is simply done with the pot, if you > require less than the control circuit will handle, > simply bypass the final stage. Most RF amplifiers > work better at the nominal operational values. > > > > The CD units faired a little better, but those > > darn ham operators could fry > > them too! Ha! Ha! > > Gary KB7TRP > > Only the Micor style msr pa's seem to be trouble below > 150Mhz. I've never had a 110 watt vhf intermittent duty > cycle pa fail when tuned down to 60 watts. Same with > the high power (semi rare) Paging MSR PA. > > The fly in the vhf msr soup is the high split msr > micor style pa. It's not happy below 150Mhz without > serious power reduction (or modification). > > cheers, > skipp Hi Skipp, You are obviously in the business, so needless to say my ignorance is probably showing. My MSR has the TLD2532A 110 watt intermittent PA. NCD is more my terminology (non continuous duty) than anything else. I got into the habit of refering to an intermittent PA as non continuous duty (NCD) by hanging around another tech that used it. He was also the one that filled me in on MSRs' PA history. (however right or wrong the info was) I was running my first PA at 60 watts when it failed. The only thing different that I'm doing now than before, is I am using fans to blow air out of the cabinet top side vents, plus a fan blowing across the PA heat sink fins. Before, I was just blowing accross the heat sink fins only. I'm not sure how efficient the PA heat sink fan is, because I had to do some creative engineering to get a fan mounted to blow up the fins from the bottom. My site owner requires repeaters to be in cabinets with covers on, and you would know how little room there is to get a fan mounted to blow on the MSR PA with the front cover on the cabinet and still do some serious air movement. It does work and looks somewhat professional. This repeater was getting heavy use at the first PA failure, but now not as much use. This may have something to do with its'longevity now. Gary KB7TRP Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
